Relationships among geomorphological variables affecting water yield from small watersheds

The objectives of this study were (1) to develop numerical expressions for geomorphological parameters affecting water yield which would be compatible with computer analysis, and (2) to determine the minimum number of parameters necessary to relate geomorphological factors to the water yield from small watersheds. Ten watersheds located in four physiographic regions of Tennessee were selected for this study. Four of the watersheds are located near Oak Ridge in the Valley and Ridge physiographic region; two are near Spring Hill in the Central Basin physiographic region; two are near Milan in the Gulf Coastal Plain physiographic region, and two are near Crossville in the Cumberland Plateau region. Seventeen numerical expressions for the selected physiographic parameters were determined from topographic maps. Numerical expressions of soil and land use were determined from USDA-SCS soil cover index numbers. Rotated factor analyses were used to find the minimum number of parameters required to represent the original variables. Seven of the seventeen parameters were found to account for most of the information contained in the variables. They were (1) area, (2) form, (3) mean elevation, (4) elevation distribution, (5) total relief, (6) mean slope, and (7) stream order one. In an analysis in which the soil cover parameter was included, this parameter was shown to be important, but not as pronounced as the others. This might have been due to the fact that the numerical differences were not great among the soil cover indices for the six watersheds for which the soil cover index was used. The depth of soil profile was also found to be a factor which should be included.